Add: brainfuck interpreter; documentation; uptime

USERS.md

@@ -12,6 +12,41 @@ Once you have launched the OS for the first time, you should first see the welco
 
 To get the list of available commands on the system, type `help`.
 
-## Next what?
+### Commands
 
-Once programs will be added, there will be more info here. For now you can just play around and make the kernel panic. That's it.
+#### `help`
+
+Shows all of the available commands, which are explained here.
+
+#### `panic`
+
+Triggers a kernel panic by trying to divide four by zero.
+
+#### `words`
+
+Prints ten random words using an arbitrary dictionary that you can expand in `src/programs/words.c`.
+
+#### `primes`
+
+Computes prime numbers up to `PRIMES_MAX`, defined in `src/programs/primes.c`.
+
+#### `rainbow`
+
+Asks for text and then outputs it with different vibrant colors.
+
+#### `clear`
+
+Clears the screen by scrolling (screen height) times.
+
+#### `math`
+
+**This program is not working!**
+The lexer and parser should be okay, but I can't figure out the `%f` floating point format specifier in the freestanding printf implementation; it triggers weird exceptions that I don't understand. So no math interpreter for now.
+
+#### `bf`
+
+A brainfuck interpreter with every instruction and default tape size (30k cells).
+
+#### `uptime`
+
+Gets system uptime from the timer in ticks. Ticks are incremented at a rate of 18.222Hz (18.222 ticks per second).